So, there's this old Asimov story

So, there's this old Asimov story

: james_nicoll; July 10th, 2012

Yeah, yeah, this got posted before I finished. Be interesting to see how many comments that gets in the couple of minutes it takes me to fix this.

In the Asimov story, someone has invented a no-gravityizer with an undocumented feature:

Objects in the field exit at the speed of light (or presumably just under it). The one guy who realizes what is going to happen puts a ~~baseball~~ billiard ball into the field, a ~~baseball~~ billiard ball that kills his bitter rival as it blasts through him at near C.

The problem with that story is the effects of a near-light-speed ~~baseball~~ billiard ball will not be limited to drilling tidy holes through things.

Also posted at Dreamwidth, where there are

comment(s); comment here or there.

( 30 comments — Leave a comment )

derekl1963

2012-07-10 06:42 pm (UTC)

timill

2012-07-10 06:45 pm (UTC)

Billiard ball. The story is called "The Billiard Ball" IIRC

scentofviolets

2012-07-10 08:56 pm (UTC)

I think it would be a mistake to assume that Asimov didn't have any idea of what would really happen in this situation. After all, his initial title - rejected by the publisher with extreme prejudice - was "Dirty Pool" ;-)

autopope

2012-07-10 06:51 pm (UTC)

Actually, the XKCD description kinda-sorta holds for a billiard ball too. Or a ping-pong ball.

At .86 of c the kinetic energy of a moving object is equal to about half its rest mass, if I remember correctly. Rest mass-energy of one kilogram is equivalent to roughly 21 megatons of TNT. Even a one gram ping-pong ball therefore has kinetic energy equal to roughly one Hiroshima-sized nuke (on the order of 10kt) and it's gonna dissipate it very rapidly indeed in air (and a victim's body).

Baseballs mass what, half a kilo?

Forget not being in the neighbourhood when the super-pitcher throws -- you don't want to be in the same city. Best watched from a range of not less than twenty kilometres, with welding goggles and a blast shield to dive behind!

Edited at 2012-07-10 06:57 pm (UTC)

jsburbidge

2012-07-10 06:59 pm (UTC)

Yep. The Asimov story has a neat circle punched through the rival -- sort of standard "ignore friction" thought-problem approach.

In real life, assuming that the field were possible, the air kicked out of the field when it started up ought to have turned the room into a blazing inferno.

scentofviolets

2012-07-10 08:51 pm (UTC)

Asimov dealt with this one: Just as the field reached the zero-gee condition, it became visible as a shaft of purple/uv light. Turns out that air molecules exiting the field at c-ish velocities were slowed down by the atmosphere and in the process emitted radiation.

Now, you may argue the actual numbers with more or less justification. But Asimov was aware of this effect and wrote it into the story. Great line too; when reporters asked what was the source of light, Bloom replied that it was a 'characteristic of the antigravity field'. Which of course was 'no answer at all' as the narrator observes ;-)

jsburbidge

2012-07-10 08:57 pm (UTC)

I did remember that, and it would probably match the steady-state of random molecules crossing the boundary. It's the initial blast which would be more of a problem. (I would also guess that the quanta emitted would be rather more energetic than UV...)

scentofviolets

2012-07-10 09:10 pm (UTC)

Like I said, now you're talking numbers.

resonant

2012-07-10 11:02 pm (UTC)

So the glow would be better described as Cerenkov radiation?

neowolf2

2012-07-11 01:01 am (UTC)

If air molecules crossing the boundary are accelerated to c, that itself would be enough to cause a massive explosion. Naively, the mass flow of air molecules across a unit surface, into a vacuum, will be (density air) * speed of sound, or about 300 kilograms per square meter per second.

Where does the energy come from, anyway? This device is perpetual motion machine of the first kind.

jsburbidge

2012-07-11 01:22 am (UTC)

IIRC, the story ends with a recognition of the energy source / perpetual motion potential.

However, I don't think the flow of air into a vacuum would be the main effect to worry about, because you wouldn't get there. The initial outflow of air when the field turned on would have a higher pressure than the inflow (the relativistic mass would be immense), and the collision effects would be well above LHC levels: particle showers, very hard photon radiation, and temperatures (though not densities) somewhere in the First Three Minutes ballpark.

neowolf2

2012-07-11 02:36 am (UTC)

For the outgoing particles to produce a pressure to compensate for the inflowing air, you'd need about 90 terawatts of radiation per square meter.

jsburbidge

2012-07-11 02:42 am (UTC)

Well, the velocity is arbitrarily close to c, so the energy available is arbitrarily close to infinite.

One can only hope, as Smith had an Arisian say regarding the effects of a translightspeed planet, that operators would be in place to limit the volume of space affected...

scentofviolets

2012-07-11 05:10 pm (UTC)

What is this compensation you speak of? You may take this cylindrical volume to be a perfect vacuum if you like. Think of air molecules disappearing at the boundary on one side of the cylinder and instantaneously reappearing on the far side . . . modulo the effects of the zero-gee field, of course.

neowolf2

2012-07-11 06:05 pm (UTC)

He was talking about the pressure of the outgoing particles countering the ambient air pressure, preventing inflow of air molecules. I was pointing out the energy that would be involved in providing this pressure.

james_nicoll

2012-07-10 07:00 pm (UTC)

During a conversation with John Schilling I discovered a pistol that fires rounds at sufficiently fine tuned interplanetary speeds within an atmosphere creates effects a lot like a traditional blaster (specifically the Doc Smith variety where heat issues require users to wear stout armour and an extended firefire sets fires to brick walls). Too high and the round dissipates all its energy very soon after it hits air but there's a nice range of velocities where the meteoric round can actually hit things at range.

james_nicoll

2012-07-10 07:01 pm (UTC)

the round dissipates all its energy very soon after it hits air

which is to say, firing it is a bit like pulling the pin on a grenade before holding it at arm's reach.

aboutlikepleats

2012-07-10 07:42 pm (UTC)

Tell me that isn't the voice of experience. Please.

james_nicoll

2012-07-10 08:27 pm (UTC)

Do homemade grenades count?

kithrup

2012-07-11 01:33 am (UTC)

Most people don't have to ask that sort of question.

krin_o_o_

2012-07-11 04:43 pm (UTC)

"Most People" is a rather rarified commodity these parts.

zxhrue

2012-07-11 05:16 am (UTC)

ahem.

"Once you have pulled the pin from Mr. Grenade, he is no longer your friend."

johnreiher

2012-07-11 06:21 am (UTC)

No, you can pull Mister Pin as much as you want. It's when Missus Spoon pops off that Mister Grenade is no longer your friend...

bschilli

2012-07-10 08:44 pm (UTC)

A baseball weighs five ounces, about 140 grams.

neowolf2

2012-07-10 08:50 pm (UTC)

The xkcd description talks about fusion, but at those speeds the kinetic energy of the nuclei far exceeds their nuclear binding energy. The nuclei would undergo spallation, shattering into smaller fragments and free protons and neutrons, together with production of pions and other mesons.

scentofviolets

2012-07-10 09:08 pm (UTC)

At 0.866 c, the kinetic energy is equal to the rest mass, not half of it. The formula (in terms of rest mass) is just gamma minus one. Setting gamma to two (so that γ-1=1, i.e., one rest mass) and solving for v gives v=0.866 c.

Reminds me of this analysis of relativistic ravioli

(Anonymous)

2012-07-11 12:19 am (UTC)

http://www.mit.edu/people/daveg/Humor/ravioli_as_gas

pauldormer

2012-07-11 11:02 am (UTC)

I do like the last line of explanation:

A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered "hit by pitch", and would be eligible to advance to first base.

krin_o_o_

2012-07-11 04:44 pm (UTC)

and second, third, outfield, and the pub down the street; all at about the same time.

radiotelescope

2012-07-11 05:11 pm (UTC)

My complaint about "The Billiard Ball" is not the energy levels (which I didn't have the math to compute when I first read it), but the direction. Surely it's obvious that if a ball rolls into a vertical field, and the molecules leave in the direction they were moving, they'll all blast *downward*.

(Okay, the shooter could apply some serious backspin -- or null-spin, I suppose -- but I believe the story was clear that the shot was low-speed.)

Yes, I have complained about this before. Probably in the 20th century on Usenet.

( 30 comments — Leave a comment )

james_nicoll

More Words, Deeper Hole

Reminds me of this analysis of relativistic ravioli